1. Technical Field of the Invention
The present invention relates to oil-in-water emulsions in which the average size of the globules which constitute the oily phase of said emulsions ranges from 100 nm to 1,000 nm, comprising inorganic nanopigments based on metal oxides and at least one organic UV-screening agent, said at least one organic UV-screening agent comprising a 4,4-diarylbutadiene UV-A sunscreen.
This invention also relates to a method for formulating these compositions and their use in the abovementioned cosmetic application.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation having wavelengths of between 280 nm and 400 nm allows tanning of the human epidermis, and that rays having wavelengths of between 280 nm and 320 nm, known by the name UV-B, cause erythemas and skin burns which can hamper the development of the natural tan; this UV-B radiation must therefore be screened out.
It is also known that UV-A rays having wavelengths of between 320 nm and 400 nm, which cause tanning of the skin, are capable of inducing its impairment, in particular in the case of a sensitive skin or a skin continually exposed to solar radiation. UV-A rays cause in particular a loss of elasticity of the skin and the appearance of wrinkles which lead to premature aging. They promote the onset of the erythematous reaction or amplify this reaction in some subjects and may even be responsible for phototoxic or photoallergic reactions. It is therefore desirable to also screen out UV-A radiation.
Numerous cosmetic compositions intended for photoprotecting the skin have been proposed to date and the use of nanopigments of metal oxides such as nanopigments of TiO2 in antisun/sunscreen products is increasingly frequent because they make it possible to obtain very high protection indices in combination with conventional UV-screening agents.
Oil-in-water emulsions are in general more highly appreciated by the consumer than water-in-oil emulsions in particular because of their pleasant feel and their presentation in the form of a non-greasy cream or milk.
One of the major disadvantages of the O/W type antisun compositions known to date and more particularly of those containing nanopigments of metal oxide, in particular of titanium, is that once applied to the skin in the form of a film, they produce thereon a lightening effect which is cosmetically undesirable and generally little appreciated by the users. This effect is all the more marked if the concentration of nanopigments in the emulsion is high and if the distribution, after application, on the skin is uneven and non-homogeneous. This poor distribution of the nanopigments which is observed at the surface of the skin is often linked to the fact that there is a substantial lack of homogeneity (poor dispersion of the pigment in its carrier) in the actual initial emulsion (before application).
To remedy this problem, specific O/W emulsions obtained according to the so-called “phase inversion” technique (PIT) have been proposed.
In order to be able to obtain good protection both in the range of UV-A rays and in the UV-B range, organic screening agents which are active in UV-A, combined with organic screening agents which are active in UV-B, are most often used in this type of composition.
Among the available organic UV-A-screening agents, a family of compounds which is particularly effective in UV-A is 1,4-benzene[di(3-methylidene-10-camphorsulphonic)] acid and its different salts, which is described in particular in FR-A-2,528,420 and FR-A-2,639,347; they are indeed capable of absorbing ultraviolet rays having wavelengths of between 280 nm and 400 nm, with absorption maxima of between 320 nm and 400 nm, in particular in the region of 345 nm.
However, the specific O/W emulsions obtained according to the so-called “phase inversion” technique containing nanopigments and UV-A-screening agents of this type lose their UV-protection efficacy and in particular UV-A-protection efficacy when they come into contact with water; indeed, these screening agents have a tendency to disappear with water, with bathing in the sea or in a swimming pool, under the shower or during the practice of water sports; thus, these antisun/sunscreen compositions no longer provide the desired initial protection when the substrate (skin or hair) to which they have been applied comes into contact with water.
Thus, the need still remains for providing antisun/sunscreen compositions of the O/W emulsion type obtained according to the so-called “phase inversion” technique based on nanopigments of metal oxides and at least one organic UV-A-screening agent of comparable efficacy to that of 1,4-benzene[di(3-methylidene-10-camphorsulphonic)] acid and its different salts which are stable over time and are resistant to water (stability to water) and whose cosmetic performance would be comparable to that obtained with conventional oil/water emulsions.